JP4052781B2 - Electrostatic ink jet head and ink jet recording apparatus - Google Patents

Description

【００５２】
図１４乃至図１６に示した平行Ｇａｐ形状のインクジェットヘッドの場合には、当接時間の比率が４０％以下の場合には振動板の当接変位量が１０％以下となり、インク吐出にほとんど影響なく、図１７乃至図２１に示したガウスＧａｐ形状のインクジェットヘッドの場合は、当接時間の比率が２０％以下の場合に、振動板の当接変位量が１０％以下（ただし、図１９の場合は１０.８２％となるが、この程度であればインク吐出にほとんど影響がない。
【００５３】
図２２は、上述のごとき本発明による静電インクジェットヘッドを搭載したインクジェット記録装置の一使用例を説明するための要部概略構成図で、図中、４０はインクジェット記録ヘッド、４１は該インクジェット記録ヘッド４０を搭載し、該インクジェット記録ヘッド４０を矢印Ｘ方向に往復動させるキャリッジ、４２は該キャリッジ４１を矢印Ｘ方向に往復動させるための駆動軸、４３は該キャリッジ４１の往復動を案内するための案内ロッド、４４は記録紙である。周知のように、キャリッジ４１の往復動によりインクジェット記録ヘッド４０を矢印Ｘ方向に往復動させるとともに、記録紙４４を矢印Ｙ方向に移動させることにより、記録紙４４上に所望の文字，図形等を印写する。
【００５４】
図２３は、本発明による静電インクジェットヘッドを駆動するのに用いて好適なヘッド駆動回路の一例を説明するための要部構成図で、図中、５０は、ヘッド駆動制御回路部、５１はカウンタ、５２はメモリ、５３はＤ／Ａコンバータ、５４はアンプ、５５はヘッド部（アクチュエータ）で、ヘッド駆動制御回路部５０は、予め記憶させておいた複数の駆動電圧波形から１つを選択して出力する。カウンタ５１及びメモリ５２にて、駆動するビット（アクチュエータ）を選択し、そのディジタルに出力信号をＤ／Ａコンバータ５３にてアナログ信号に変換し、アンプ５４にて増幅し、ヘッド（アクチュエータ）５５を駆動する。
【００５５】
【発明の効果】
静電インクジェットヘッドにおける振動板と個別電極との間に印可するパルス電圧の１画素を形成するのに要する時間に対する割合（実質的には、振動板が電極に当接している時間割合）を適切に選択することにより、更には、Ｇａｐ室と振動室との割合を適切に選択することにより、静電インクジェットヘッドの周波特性を大幅に改善し、インク吐出特性の安定性を向上させ、延いては、ヘッドの信頼性を高めることができる。
【図面の簡単な説明】
【図１】 本発明が適用される静電力を利用したインクジェットヘッドを説明するための要部斜視図である。
【図２】 図１に示したインクジェットヘッドの１つのアクチュエータの構成を示す断面図（図１のII−II線断面図）である。
【図３】 本発明が解決しようとする、静電インクジェットヘッドの課題を説明するための要部概略断面図である。
【図４】 振動板と電極との間に印加するパルス電圧の例を示す図である。
【図５】 本発明が適用される静電インクジェットヘッドの短辺方向のギャップ形状の例を示す図である。
【図６】 平行Ｇａｐの静電インクジェットヘッドにおける周波数依存性（周波数をパラメータとした、印加パルス電圧と振動板の変位量の関係）を示す図である。
【図７】 平行Ｇａｐの静電インクジェットヘッドにおけるパルス幅・周波数依存性（パルス幅を変えた周波数をパラメータとした印加パルス電圧と振動板の変位量との関係）を示す図である。
【図８】 非平行Ｇａｐの静電インクジェットヘッドにおける周波数依存性（周波数をパラメータとした、印加パルス電圧と振動板の変位量の関係）を示す図である。
【図９】 非平行Ｇａｐの静電インクジェットヘッドにおけるパルス幅・周波数依存性（パルス幅を変えた周波数をパラメータとした印加パルス電圧と振動板の変位量との関係）を示す図である。
【図１０】 Ｇａｐ室未封止（Ｖｌ／Ｖ＝０.８）の静電インクジェットヘッドにおける周波数依存性を示す図である。
【図１１】 Ｇａｐ室封止（Ｖｌ／Ｖ＝０.８）の静電インクジェットヘッドにおける周波数依存性を示す図である。
【図１２】 Ｇａｐ室未封止（Ｖｌ／Ｖ＝０.６）の静電インクジェットヘッドにおける周波数依存性を示す図である。
【図１３】 Ｇａｐ室封止（Ｖｌ／Ｖ＝０.６）の静電インクジェットヘッドにおける周波数依存性を示す図である。
【図１４】 平行Ｇａｐ、当接時間４.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図１５】 平行Ｇａｐ、当接時間６.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図１６】 平行Ｇａｐ、当接時間１０.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図１７】 ガウスＧａｐ形状、当接時間４.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図１８】 ガウスＧａｐ形状、当接時間６.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図１９】 ガウスＧａｐ形状、当接時間１０.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図２０】 ガウスＧａｐ形状、当接時間２０.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図２１】 ガウスＧａｐ形状、当接時間３０.０μｓにおける静電インクジェットヘッドの周波数依存性を示す図である。
【図２２】 本発明による静電インクジェットヘッドを搭載したインクジェット記録装置の一例を示す要部斜視図である。
【図２３】 本発明の実施に使用される駆動電圧パルス発生回路の一例を説明するための図である。
【符号の説明】
１０…電極基板、１１…個別電極、１２…保護膜、１３…封止材、２０…液室・振動板基板、２１…インク液室、２２…振動板、３０…ノズル基板、３１…ノズル。[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an electrostatic ink jet head using a microactuator using electrostatic force.And inkjet recording apparatusAbout.
[0002]
[Prior art]
FIG. 1 is a perspective view of an essential part for explaining an inkjet head using electrostatic force to which the present invention is applied, and FIG. 2 is a cross-sectional view showing a configuration of one actuator of the inkjet head shown in FIG. 1 is an electrode substrate, 10 is a liquid chamber / vibration plate substrate, 30 is a nozzle substrate (this nozzle substrate 30 is shown removed in FIG. 1). As is well known, the nozzle substrate 30 is provided with a nozzle 31, and the liquid chamber / vibration plate substrate 20 is provided with an ink liquid chamber 21 communicating with the nozzle 31. A conductive diaphragm 22 is provided which functions as a part of the chamber 21 and a part of the common electrode, and is thin and low in rigidity so as to be variable. The electrode substrate 10 has individual electrodes 11 disposed with a predetermined gap from the vibration plate 22 with respect to the vibration plate 22 and outside the ink liquid chamber 21. In addition, 12 is a protective film for preventing a short circuit between the individual electrode 11 and the diaphragm 22, and 13 is a sealing material for sealing the opening of the space in which the individual electrode 11 is disposed. As shown in FIG. 1, an electrostatic ink jet head to which the present invention is applied has a plurality of actuators as shown in FIG. 2, and ink droplets are ejected from each actuator. .
[0003]
1 and 2, when a voltage is applied between the diaphragm 22 and the individual electrode 11, the diaphragm 22 is displaced to the electrode 11 side by an electrostatic force. Here, when the applied voltage is turned OFF, the diaphragm 22 returns to the position before the original voltage application. An electrostatic ink jet utilizes the mechanical behavior of the diaphragm 22 with respect to the electrostatic force as an ink ejection force of the ink jet. In FIG. 2, the space between the substrate 20 having the diaphragm 22 and the individual electrode 11 is generally sealed with a sealing material 13 in order to isolate it from the outside. The space is referred to as a Gap (gap) chamber. Further, in this gap chamber, a portion corresponding to the portion immediately below the diaphragm is referred to as a vibration chamber.
[0004]
In the electrostatic ink jet head as described above, when a voltage is applied between the diaphragm 22 and the individual electrode 11, the diaphragm 22 is displaced by an electrostatic force acting between the diaphragm 22 and the individual electrode 11. In such an electrostatic actuator, the driving voltage is reduced by reducing the thickness of the diaphragm 22. As a result, the driving voltage can be lowered, but the diaphragm is thin, so that the rigidity of the diaphragm is low. For this reason, the presence of air (or other gas) in the vibration chamber or the gap chamber greatly affects the behavior. For example, when the diaphragm 22 approaches the electrode 11, it receives a compression resistance of air, so that the voltage at which the diaphragm 22 abuts on the electrode 11 (hereinafter referred to as a contact voltage) is static. Compared to the above, it becomes larger when it is dynamic.
[0005]
[Problems to be solved by the invention]
The present invention has been made for the purpose of dealing with another major problem described below, which is caused by the presence of air as described above.
[0006]
3 (A) and 3 (B) are schematic configuration diagrams of the main part for explaining the problems of the electrostatic ink jet head that the present invention intends to solve. FIG. 3 (A) shows a case where the drive frequency is low. FIG. 3B is a diagram showing a displacement amount (d) of the diaphragm 22 when the drive frequency is high. The diaphragm 22 of the electrostatic ink jet head (22 'indicates a state in which the diaphragm 22 is displaced and is in contact with the individual electrode 11) is required to vibrate dynamically on the order of -10 kHz, and therefore Originally, the volume of the vibration chamber is small, and the vibration plate 22 moves within the vibration chamber. Therefore, as described above, the vibration plate 22 receives air compression resistance, while the air that has once exited the vibration chamber (indicated by the arrow). Has a characteristic that it is difficult to return to the vibration chamber again. If the driving conditions (the shape of the driving voltage pulse) are the same, it depends on the frequency of the driving voltage pulse, and the higher the frequency, the greater the amount of air that comes out of the vibration chamber and cannot return to the vibration chamber, The vibration position approaches the electrode 11 side.
[0007]
FIG. 6 is a diagram showing a driving result of a conventional electrostatic ink jet head. As shown in FIG. 6, as the frequency is increased, the amount of air that cannot be returned from the vibration chamber increases. As a result, FIG. As shown in (B), the diaphragm 22 vibrates at a position closer to the electrode 11, which substantially reduces the distance between the electrode 11 and the diaphragm 22, and the contact voltage decreases. It is shown that. Thus, the frequency characteristics that did not become a problem when the drive frequency is low become obvious when the frequency is increased. This phenomenon is peculiar to the electrostatic actuator in which the diaphragm is driven by electrostatic force, and is a problem to be solved when high frequency driving is performed.
[0008]
Note that the above-described problem is based on the premise that the diaphragm is in a contact drive in contact with the electrode. The non-contact driving without contact does not cause the above-described problem of frequency dependence or does not cause a problem.
[0009]
As described above, in the electrostatic inkjet head, there is a problem that the diaphragm receives a compression resistance due to the presence of air in the gap chamber, thereby increasing the contact voltage. Several measures are shown. As an example, JP-A-7-299908 can be cited. In this case, a space where air escapes is provided in a gap chamber other than the vibration chamber so as not to receive air compression resistance when the vibration plate is displaced to the electrode side. The volume ΔV excluded by the diaphragm and the volume V of the gap chamber are defined in relation to each other.
[0010]
However, no countermeasures have been proposed for the above-described problems that become apparent in high-frequency driving. This is considered to be due to the fact that in the conventional electrostatic ink jet head, the maximum drive frequency was set to about 10 kHz at the most, and it was difficult for the problems described above to become obvious.
[0011]
The present invention has been made in view of the above circumstances, and relates the above-described vibration chamber volume and Gap chamber volume, and further aims to reduce the Gap chamber volume other than the vibration chamber, This is different from the invention disclosed in Japanese Patent Laid-Open No. 7-299908.
[0012]
Furthermore, the present invention improves the frequency dependence of the electrostatic actuator only by setting the drive voltage waveform.
Sufficiently improving the frequency dependence of an actuator with a gap shape, changing the configuration and specifications of the actuator to improve the frequency dependence of the electrostatic actuator,
Improve the frequency dependence of the electrostatic actuator by changing the actuator configuration and specifications and setting the drive voltage waveform.
This is for the purpose of sufficiently improving the frequency dependency of a certain gap actuator.
[0013]
[Means for Solving the Problems]
  The invention of claim 1 is directed to a diaphragm and the diaphragm.Gan electrode disposed with ap, a pulse voltage is applied between the electrode and the diaphragm to displace the diaphragm by electrostatic force, and ink droplets are ejected by the mechanical restoring force of the diaphragm. An electrostatic inkjet head for jetting,The electrode is formed in an arc shape in which a central portion is convex in the diaphragm direction in the diaphragm short side direction.It is characterized byThe
[0022]
  Claim2The invention of claim1In the invention ofGap formed ofThe chamber is sealed with a sealing material.
[0026]
  Claim3The invention of claim 1Or 2An ink jet recording apparatus comprising: the electrostatic ink jet head described above, wherein the electrostatic ink jet head is opposed to a recording paper, and ink droplets are ejected to perform recording.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an electrostatic ink jet head as shown in FIGS. 1 and 2, that is, a nozzle 31, an ink liquid chamber 21 communicating with the nozzle 31, a part of the ink liquid chamber 21, and a common electrode. The diaphragm 22 provided as a part, and the individual electrode 11 provided with a predetermined gap outside the ink liquid chamber 21 so as to face the diaphragm 22, and the diaphragm 22 and the individual electrode 11 When a pulse voltage is applied between the diaphragm 22 and the individual electrode 11 to generate an electrostatic force, the diaphragm 22 is deformed by the electrostatic force, and the application of the pulse voltage is canceled. In an electrostatic ink jet head having a plurality of bits of an electrostatic actuator capable of ejecting ink droplets from the nozzle 31 by a mechanical restoring force generated on the plate 22, one pixel is applied with a pulse voltage. In this case, the time required for the diaphragm 22 and the electrode 11 to abut against the time required to form one pixel is set to 40% or less so that the frequency dependence can be largely suppressed. Is.
[0028]
Initially, the cause of the frequency dependence described above could not be grasped. However, according to many verification examples including experimental data to be described later in Example 1, it has been found that the above-described problem depends on the ratio of the time for which the diaphragm 22 contacts the electrode 11 in one pixel time. That is, the frequency dependency is one aspect of the dependency on the ratio of the contact time in one pixel time (hereinafter referred to as contact time / 1 pixel time dependency). Here, one pixel time includes one pixel or one pixel, that is, a case where a dot formed by a plurality of droplets is recognized as one pixel even if it is not a circle or one dot. This is the time for forming a pixel.
[0029]
4A, 4 </ b> B, and 4 </ b> C are diagrams illustrating examples of drive voltage pulses applied between the diaphragm 22 and the individual electrode 11, and a plurality of drive voltages can be applied to one pixel even with one pulse. FIG. 4A shows an example in which only one positive driving pulse is used to form one pixel by one driving pulse, and FIG. 4B shows positive and negative (even if a negative pulse is used). FIG. 4 shows an example in which the vibration plate is formed by a driving pulse (which is to remove the residual charge peculiar to the electrostatic ink jet head when a positive / negative voltage pulse is applied in this way). (C) shows an example in which a single-element is formed by a plurality of voltage pulses (that is, a plurality of ink droplets). Here, when one pixel is formed by a plurality of pulses, the ink dots do not need to be circular on the recording medium, and further, it is not necessary to form a single dot by merging completely. As long as the configuration is such that almost one pixel is formed. Although not shown, there may be a configuration in which a non-zero voltage is applied when ink is not ejected. However, in the present invention, the drive voltage is a voltage at which the diaphragm abuts on the electrode, and forms one pixel by abutting once for 1 pulse / 1 pixel and n times for n pulse / 1 pixel. become. For example, in the example shown in FIGS. 4A and 4B, the driving condition is one pulse / one pixel, and the maximum driving frequency is 1 / T (where T is the time required to form one pixel). ). On the other hand, in the example shown in FIG. 4C, the driving condition is a plurality of pulses / one pixel, and the maximum driving frequency is not 1 / T but 1 / T1.
[0030]
In the present invention, in the one pixel time T as described above, the time for which the diaphragm 22 contacts the electrode 11 is 40% or less of the time T required to form one pixel. As an example, even if the time during which the diaphragm 22 contacts the electrode 11 is 40% or more of T1 within the driving time T1 with respect to the maximum driving frequency, if it is 40% or less within one pixel time T, The effect of the present invention, that is, the frequency dependency can be suppressed.
[0031]
The higher the drive frequency, the narrower the margin for setting the drive voltage pulse width. As a result, ink ejection with the best performance of the head is realized by taking into account the natural frequency and meniscus vibration caused by the head configuration. You may not be able to select a pulse width that you can. However, even if the ink ejection efficiency is somewhat sacrificed, the total ink ejection efficiency and frequency characteristics are clearly better when the configuration of the present invention is adopted.
[0032]
[Example 1]
Electrostatic actuator specifications:
The basic configuration of the head is as shown in FIGS. The electrode substrate 10 was engraved by etching (gap chamber), and the individual electrode 11 was formed thereon using TiN. On the electrode 11, as a protective film 12, SiO₂Formed. Further, the Si substrate 20 was engraved by etching (liquid chamber 21), and the thin plate formed thereby was used as the diaphragm 22. An electrostatic ink jet head was formed by bonding the two substrates 10 and 20.
[0033]
FIG. 5 is a diagram showing an example of the gap shape of the electrostatic ink jet head to which the present invention is applied. FIG. 5A shows a parallel gap in which the individual electrodes 11 are arranged in parallel to the diaphragm 22. FIG. 5B is a diagram showing a non-parallel central convex Gap in which the central portion of the individual electrode 11 is close to the diaphragm 22, and FIG. 5C is an individual diagram with respect to the diaphragm 22. This is a non-parallel central concave gap in which the central portion of the electrode 11 is separated.
[0034]
Diaphragm-electrode gap: parallel gap shown in FIG.
Gap length: 0.25 μm
Diaphragm thickness: 3 μm
Diaphragm area: 130 μm × 2000 μm
[0035]
6 to 13 are all measured with a laser Doppler vibrometer for the vibration displacement at the center in the short side direction of the diaphragm. The horizontal axis represents the magnitude of the drive voltage, and the drive voltage waveform is a rectangular wave. The drive frequency is the highest drive frequency in the present invention. In each drawing and each driving condition, there is a region where the increase in displacement is almost saturated at a certain voltage or higher. The displacement amount at the time of saturation is the contact displacement amount.
[0036]
Evaluation results:
As shown in FIG. 6, if the driving pulse conditions (rising Pr = 1 μs, pulse width Pw = 10 μs, falling Pf = 0 μs; hereinafter referred to as 10 (1,0)), the frequency increases. As a result, the amount of displacement (hereinafter referred to as the amount of contact displacement) when the diaphragm contacts the electrode decreases, and the contact voltage decreases. However, as described above, this is not a frequency dependency but a contact time / 1 pixel time dependency. Therefore, as shown in FIG. 7, if the drive voltage pulse width is 40% or less of 1 pixel time (16.6 μs at 60 kHz) (6 μs in FIG. 7), for example, even if the drive frequency is 60 kHz, 2 kHz The contact displacement amount can be suppressed to a decrease of about 10% with respect to the case (see the graph of FIG. 7). At this level, Vj and Mj can be kept within the specification error range during ink ejection. Here, it is mentioned that the drive voltage pulse width and the contact time are almost the same, although depending on the conditions.
[0037]
The optimum pulse width of the drive voltage in an electrostatic inkjet head varies depending on the amount of ink liquid to be ejected and the ejection efficiency of the head in consideration of the fluid characteristics of the ink, but it seems that a pulse width of about 5 to 20 μs is used. It is. In FIG. 6, a pulse width voltage of 10 μs was used. Here, at 30 kHz where the contact time for one pixel time is about 33%, the contact displacement amount for 2 kHz is reduced by about 15%. Considering the pulse width up to about 20 μs, it is feared that the contact displacement amount is reduced by 10% or more at 2 kHz at least at 20 kHz or more. If the displacement reduction is about 10%, the ink ejection efficiency is hardly affected, but if it is 15% or more, the influence starts to occur. When the amount of displacement is reduced by 30%, the ink ejection characteristics clearly change.
[0038]
When the time for which the diaphragm is in contact with the electrode is 20% or less in one pixel time, the contact time / 1 pixel time dependency can be largely suppressed without depending on the gap shape between the diaphragm and the electrode.
As shown in FIGS. 5 (A) and 5 (B), when the gap length with respect to the substantially central portion of the diaphragm having a gap shape of parallel, non-parallel central convex or parallel on one side and central convex on one side is minimum A sufficient improvement of the contact time / 1 pixel time dependency can be obtained under the above-described driving condition of 40% or less. However, as shown in FIG. 5C, when the gap length with respect to the substantially central portion of the diaphragm such as the non-parallel central concave or the one-side parallel and one-side non-parallel central concave is maximum as shown in FIG. Even in the case of a gap, when the gap length is very narrow as 0.3 μm or less, there may be a case where sufficient contact time / one pixel time dependency cannot be improved under the above-described driving condition of 40% or less. is there. One reason for this is that since the ratio Vla / Vl of the vibration chamber volume Vla when the diaphragm abuts and the vibration chamber volume Vl when the voltage is OFF is small, the effect of air exiting from the vibration chamber becomes relatively large. This is probably because of this. Thus, if the contact time in one pixel time is 20% or less, the contact time / 1 pixel time dependency can be suppressed without depending on the gap shape.
[0039]
Of course, as the maximum frequency is increased, narrowing the pulse width so that the contact time is 20% or less may reduce the ink ejection efficiency of the head at a low frequency. However, when the configuration according to the present invention is adopted, the total ink ejection efficiency and frequency characteristics are clearly improved.
[0040]
The following points are pointed out here. The configuration shown in FIG. 5B is convenient for reducing the compression resistance of the air received by the diaphragm when the diaphragm contacts the electrode. In order to reduce the compression resistance of air, it is necessary to provide an air escape place. However, this escape place is not provided in a Gap chamber other than the vibration chamber as in the invention described in the above-mentioned JP-A-7-299908. Instead, it is more effective to provide it in the vibration chamber. This is because the air flow cannot follow the rapid movement of the diaphragm, and as a result, the presence of the gap chamber other than the vibration chamber cannot achieve the purpose of reducing the compression resistance of the air. Furthermore, it is because the air that has exited from the vibration chamber is difficult to return to the vibration chamber, and causes a contact time / one pixel time dependency of the actuator. Therefore, in order to reduce the compression resistance of the air, the electrode portion facing the central portion in the short side direction of the diaphragm that works the electrostatic force most effectively on the diaphragm is brought closest to the diaphragm, and the gap lengths at both ends thereof are set. The configuration shown in FIG. 5B, which is greatly adopted, is effective.
[0041]
[Example 2]
Electrostatic actuator specifications:
The basic configuration of the head is as shown in FIGS. The electrode substrate 10 was engraved by etching (gap chamber), and the individual electrode 11 was formed thereon using TiN. On the electrode 11, as a protective film 12, SiO₂Formed. Further, the Si substrate 20 was engraved by etching (ink liquid chamber), and the thin plate formed thereby was used as the diaphragm 22. An electrostatic head was formed by bonding both the substrates 10 and 20.
[0042]
Diaphragm-electrode gap: non-parallel center concave gap shown in FIG.
Maximum gap length: 0.3 μm
Diaphragm thickness: 3 μm
Diaphragm area: 130 μm × 3000 μm
[0043]
Evaluation results:
As shown in FIG. 8, if the driving pulse conditions (Pr = 1 μs, Pw = 10 μs, Pf = 0 μs; hereinafter referred to as 10 (1, 0)) are the same, the contact displacement is increased as the frequency is increased. The amount decreases and the contact voltage decreases. This is the contact time / 1 pixel time dependency. The difference from FIG. 6 which is the result of the parallel gap actuator is that the contact time / one pixel time dependency is larger in FIG. Further, in FIG. 6, the amount of displacement increases discontinuously at a certain voltage, whereas in FIG. 8, it is somewhat continuous. In FIG. 9, when the drive voltage pulse width is 40% or less of 1 pixel time (16.6 μs at 60 kHz) (6 μs in FIG. 9), 2 kHz (pulse width is 10 μs in FIG. 9). On the other hand, the amount of contact displacement is reduced by 10% or more, and the contact voltage is also clearly reduced. This causes a clear difference in ink ejection characteristics. On the other hand, when the pulse width is 20% or less of one pixel time (3 μs in FIG. 9), for example, even when the drive frequency is 60 kHz, the contact displacement amount is suppressed to a decrease within 10% as compared with the case of 2 kHz. The contact voltage is almost unchanged. At this level, Vj and Mj can be kept within the specification error range during ink ejection. However, it should be mentioned that the drive voltage pulse width and the contact time are almost the same, although depending on the conditions.
[0044]
  When the volume of the gap chamber that refers to the space formed by the substrate having the electrode and the diaphragm and the sealing material is V, and the volume of the vibration chamber that refers to the space between the electrode and the diaphragm is Vl, the following relational expression Vl / A configuration satisfying V> 0.7 is adopted. Thereby, the contact time / 1 pixel time dependency can be greatly improved.
  This is because the space of the gap chamber other than the vibration chamber is small, and there is no place for the air that should come out of the vibration chamber when the vibration plate vibrates. As a result, almost no air comes out of the vibration chamber. It is done.
  Therefore, of course, Vl / V =1. Although it is most desirable to set it to 0, it is difficult in reality, and if the relational expression is seen, a sufficient effect can be obtained.
  However, the gap chamber that is a problem in the present invention is a space that includes the vibration chamber and is blocked from the outside air by the sealing material 13. Even if it is formed of a substrate having the individual electrodes 11 and the diaphragm 22, a portion that is not blocked from the outside air by the sealing material 13 is not a gap chamber.
[0045]
Example 3
Electrostatic actuator specifications:
The basic configuration of the head is as shown in FIGS. The electrode substrate 10 was engraved by etching (gap chamber), and the individual electrode 11 was formed thereon using TiN. On the electrode 11, as a protective film 12, SiO₂Formed. Further, the Si substrate 20 was engraved by etching (liquid chamber), and the thin plate formed thereby was used as the diaphragm 22. An electrostatic head was formed by bonding both the substrates 10 and 20. After bonding, an actuator in which the opening of the Gap chamber was sealed with an epoxy adhesive 13 and an actuator that was not sealed were formed.
[0046]
Diaphragm-electrode gap: non-parallel center concave gap shown in FIG.
Maximum gap length: 0.3 μm
Diaphragm thickness: 3 μm
Diaphragm area: 130 μm × 3000 μm
Vibration chamber and Gap chamber: The actuator is designed so that the vibration chamber volume is 0.8, 0.6 with respect to the Gap chamber volume 1.0 by sealing the opening of the Gap chamber. Here, even in the case of non-sealing, the gap chamber portion in the case of the sealing bit is referred to as a gap chamber for convenience.
[0047]
Evaluation results:
FIG. 10 and FIG. 11 show the evaluation results of the unsealed actuator (FIG. 10) and the sealed actuator (FIG. 11) in the actuator where Vl / V = 0.8 by sealing. FIG. 12 and FIG. 13 show the evaluation results of the unsealed actuator (FIG. 12) and the sealed actuator (FIG. 13) in the actuator where Vl / V = 0.6 by sealing.
10 and 11, it is understood that the frequency dependency, that is, the contact time / 1 pixel time dependency can be sufficiently improved if the condition of Vl / V = 0.8 is satisfied. At this level, the ink ejection characteristics can be controlled within the specification error.
On the other hand, FIG. 12 and FIG. 13 show that the frequency dependency, that is, the contact time / 1 pixel time dependency cannot be improved when Vl / V = 0.6.
[0048]
The time for the diaphragm 22 to contact the electrode 11 was set to 40% or less in one pixel time. Furthermore, the volume of the gap chamber that refers to the space formed by the substrate 20 having the individual electrode 11 and the diaphragm 22 and the sealing material 13 is V, and the volume of the vibration chamber that refers to the space between the individual electrode 11 and the diaphragm 22. Is set to Vl, a configuration satisfying the following relational expression Vl / V> 0.7 is adopted. As a result, the contact time / 1 pixel time dependency can be drastically improved.
[0049]
In the region where the maximum driving frequency is high, in the present invention, 20 kHz or more, the time for which the diaphragm contacts the electrode is set to 20% or less in one pixel time. Further, when the volume of the gap chamber which refers to the space formed by the substrate having the electrode and the diaphragm and the sealing material is V, and the volume of the vibration chamber which refers to the space between the electrode and the diaphragm is Vl, the following relational expression: A configuration satisfying Vl / V> 0.7 is adopted. Thereby, the contact time / 1 pixel time dependency can be remarkably improved without depending on the gap shape between the diaphragm and the electrode.
[0050]
FIGS. 14 to 21 are additional experimental data, and these experiments are diagrams showing the relationship between the driving voltage of the diaphragm and the amount of displacement when the contact frequency is made constant and the driving frequency is further increased. FIGS. 14 to 16 show that the contact time is 4.0 μs (FIG. 14), 6.0 μs (FIG. 15), and 10.0 μs with respect to the parallel Gap-shaped inkjet head (see FIG. 5A). FIG. 17 to FIG. 21 show the contact time of 4.0 μs (FIG. 17), 6.0 μs (FIG. 18) with respect to the Gaussian Gap-shaped inkjet head (see FIG. 5C), FIG. 19 is a characteristic diagram when 10.0 μs (FIG. 19), 20 μs (FIG. 20), and 30 μs (FIG. 21). Show. The ink jet head used in the additional experiment shown in FIGS. 14 to 21 is different from the ink jet head used in the experiment shown in FIGS. 6 to 13, and the scale value of the head is shown in Table 1. As shown, the contact time is not the drive voltage pulse width but the actual contact time.
[0051]
[Table 1]

[0052]
In the case of the parallel Gap-shaped inkjet head shown in FIGS. 14 to 16, when the contact time ratio is 40% or less, the contact displacement amount of the diaphragm is 10% or less, which has almost no influence on ink ejection. In the case of the Gauss Gap-shaped inkjet head shown in FIGS. 17 to 21, when the contact time ratio is 20% or less, the contact displacement amount of the diaphragm is 10% or less (however, in FIG. 19). In this case, it is 10.82%, but if it is this level, there is almost no influence on the ink ejection.
[0053]
FIG. 22 is a schematic configuration diagram of an essential part for explaining an example of use of an ink jet recording apparatus equipped with the electrostatic ink jet head according to the present invention as described above, in which 40 is an ink jet recording head and 41 is the ink jet recording. A carriage on which the head 40 is mounted and reciprocates the ink jet recording head 40 in the direction of arrow X, 42 is a drive shaft for reciprocating the carriage 41 in the direction of arrow X, and 43 guides the reciprocation of the carriage 41. The guide rod 44 for recording is recording paper. As is well known, the ink jet recording head 40 is reciprocated in the direction of the arrow X by the reciprocating movement of the carriage 41 and the recording paper 44 is moved in the direction of the arrow Y, whereby desired characters, figures, and the like are placed on the recording paper 44. Imprint.
[0054]
FIG. 23 is a main part configuration diagram for explaining an example of a head driving circuit suitable for driving the electrostatic ink jet head according to the present invention. In FIG. 23, reference numeral 50 denotes a head driving control circuit part, and 51 denotes a head driving control circuit part. Counter, 52 is a memory, 53 is a D / A converter, 54 is an amplifier, 55 is a head unit (actuator), and the head drive control circuit unit 50 selects one of a plurality of drive voltage waveforms stored in advance. And output. The bit (actuator) to be driven is selected by the counter 51 and the memory 52, the digital output signal is converted into an analog signal by the D / A converter 53, amplified by the amplifier 54, and the head (actuator) 55 is To drive.
[0055]
【The invention's effect】
Appropriate ratio of the pulse voltage applied between the diaphragm and the individual electrodes in the electrostatic ink jet head to the time required to form one pixel (substantially the ratio of the time when the diaphragm is in contact with the electrode) In addition, by appropriately selecting the ratio between the gap chamber and the vibration chamber, the frequency characteristics of the electrostatic inkjet head can be greatly improved, the stability of the ink ejection characteristics can be improved, and Can improve the reliability of the head.
[Brief description of the drawings]
FIG. 1 is a perspective view of an essential part for explaining an inkjet head using electrostatic force to which the present invention is applied.
2 is a cross-sectional view (a cross-sectional view taken along the line II-II in FIG. 1) showing a configuration of one actuator of the ink jet head shown in FIG. 1;
FIG. 3 is a schematic cross-sectional view of a main part for explaining a problem of an electrostatic ink jet head which is to be solved by the present invention.
FIG. 4 is a diagram illustrating an example of a pulse voltage applied between a diaphragm and an electrode.
FIG. 5 is a diagram showing an example of a gap shape in a short side direction of an electrostatic ink jet head to which the present invention is applied.
FIG. 6 is a diagram showing frequency dependence (a relationship between an applied pulse voltage and a displacement amount of a diaphragm using a frequency as a parameter) in a parallel Gap electrostatic inkjet head.
FIG. 7 is a diagram showing pulse width / frequency dependence (a relationship between an applied pulse voltage with a frequency of which the pulse width is changed as a parameter and a displacement amount of the diaphragm) in a parallel gap electrostatic inkjet head.
FIG. 8 is a diagram showing frequency dependence (relationship between applied pulse voltage and vibration plate displacement using frequency as a parameter) in a non-parallel gap electrostatic inkjet head.
FIG. 9 is a diagram showing pulse width / frequency dependency (relationship between an applied pulse voltage using a frequency with a changed pulse width as a parameter and a displacement amount of a diaphragm) in a non-parallel gap electrostatic inkjet head.
FIG. 10 is a diagram showing frequency dependence in an electrostatic ink jet head in which a gap chamber is not sealed (Vl / V = 0.8).
FIG. 11 is a diagram showing frequency dependence in an electrostatic ink jet head sealed with a gap chamber (Vl / V = 0.8).
FIG. 12 is a diagram showing frequency dependence in an electrostatic ink jet head in which a gap chamber is not sealed (Vl / V = 0.6).
FIG. 13 is a diagram showing frequency dependence in an electrostatic ink jet head sealed with a gap chamber (Vl / V = 0.6).
FIG. 14 is a diagram showing the frequency dependence of the electrostatic inkjet head at a parallel gap and a contact time of 4.0 μs.
FIG. 15 is a diagram showing the frequency dependence of the electrostatic ink-jet head at a parallel gap and a contact time of 6.0 μs.
FIG. 16 is a diagram showing the frequency dependence of the electrostatic ink-jet head at a parallel gap and a contact time of 10.0 μs.
FIG. 17 is a diagram showing the frequency dependence of the electrostatic inkjet head in a Gaussian gap shape and a contact time of 4.0 μs.
FIG. 18 is a diagram showing the frequency dependence of the electrostatic ink jet head in a Gaussian gap shape and a contact time of 6.0 μs.
FIG. 19 is a diagram showing the frequency dependence of the electrostatic inkjet head in a Gaussian gap shape and a contact time of 10.0 μs.
FIG. 20 is a diagram showing the frequency dependence of the electrostatic inkjet head in a Gaussian gap shape and a contact time of 20.0 μs.
FIG. 21 is a diagram showing the frequency dependence of the electrostatic inkjet head in a Gaussian gap shape and a contact time of 30.0 μs.
FIG. 22 is a perspective view of a principal part showing an example of an ink jet recording apparatus equipped with an electrostatic ink jet head according to the present invention.
FIG. 23 is a diagram for explaining an example of a drive voltage pulse generation circuit used in the implementation of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Electrode substrate, 11 ... Individual electrode, 12 ... Protective film, 13 ... Sealing material, 20 ... Liquid chamber / vibrating plate substrate, 21 ... Ink liquid chamber, 22 ... Vibrating plate, 30 ... Nozzle substrate, 31 ... Nozzle.

Claims (3)

A diaphragm and an electrode disposed with a gap facing the diaphragm; applying a pulse voltage between the electrode and the diaphragm to displace the diaphragm by electrostatic force; An electrostatic ink jet head that ejects ink droplets by a mechanical restoring force of a vibration plate , wherein the electrode is formed in an arcuate shape with a central portion protruding in the vibration plate direction in the short side direction of the vibration plate An electrostatic inkjet head characterized by the above. The electrostatic ink jet head according to claim 1 , wherein the gap chamber in which the gap is formed is sealed with a sealing material. Equipped with an electrostatic inkjet head according to claim 1 or 2, it is opposed to electrostatic ink-jet head to recording paper, ink jet recording apparatus and performs recording by ejecting ink droplets.

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